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' Feb. 7, 1928. 1,65%,327

H. F. DODGE STETHOSCOPIC APPARATUS Filed May 29. 1924 Patented Feb. 7, 1928.

UNITED STATES EFHQE.

HAROLD I. DODGE, OF NEW YORK, N; Y., ASSIGNOB TO WESTERN ELECTRIC COHPAH'Y, INCORPORATED, OF YORK, N. Y., A CORPORATION OF NEW YORK.

STE'IHOSCOPIO APPARATUS.

Application filed May 29,

This invention relates to stethoscopes and has for its object to provide a stethoscope or pick-u device of high quality which is par ticula'r y sensitive to vibrations roduced within the body while substantia y unresponsive to extraneous sounds.

Heretofore, the vibratory system of stethoscopes was commonly coupled to the body acoustically by means of an air chamber between the flesh and the vibratory member. The usual air chamber, formed by the instrument itself holding the vibrating member out of contact with the body rovides very ineflicient coupling between t e flesh and the vibrating member, but a fairly eflicient coupling with the surrounding air, with the result that extraneous noises are readily picked up in spite of the fact that sometimes the air chamber is surrounded by heavy walls. There is also a multiple reflection of the sound wavesin such air chambers which interferes with the sounds of interest. With this form of coupling the ratio of useful sound energy to noise energy is low, hence it is diflicult for a physician to detect. or

focus his attention on the faint chest sounds. It has been found by providing a suitable coupler or mechanical transformer between the flesh and the vibratory member of the stethoscopic device that the energy transferred to the latter may be increased 20 to times depending upon the nature of the area of auscultation. With a suitable form of flexible vibratory member the device may at the same time be made very inefficient for picking up extraneous sound.

Preferably the coupler or mechanical transformer, should have a characteristic mechanical impedance to sound vibrations.

between the characteristic impedance of flesh and the impedance of the vibratory member. 1 l

A feature of the invention provides an electrical stethoscopic apparatus having a vibratory system of such material and proportions that the impedance looking into said s stem is substantially the same as the impe ance looking into the flesh with which it makes contact, i. e., the impedances in both directions from the point of contact are matched and substantially equal, thereby providin close mechanical coupling with the fles but loose coupling with the all.

1924. Serial No. 716,840.

In its preferred fdrm, the invention provides an electromagnetic stethoscopic pickup device having a narrow vibratory member or armature which carries a mass of soft elastic material such as gum rubber, providing a tapered mechanical impedance from the flesh to the armature. The case of the instrument may also be rovided with a holder or handle of very el aStic material to absorb extraneous vibrations caused by relative motions of the ausculators hand and body of the patient;

Referring to the drawings, Fig. 1 is a planwiew of the stethoscopic device emod ing the invention;

ig. 2 is a cross-sectional view of the device shown in Fig. 1;

Fig. 31s a plan view of another embodiment of the invention;

Fig. 4.- is a cross-sectionalview of the dev1ce shown in Fig. 3;

Figs. 5 and 6 show a miniature stethoscopic device embodying the invention; and

Fig. 7 shows a system in which the device may be used.

In a case 10 is provided a permanent magnet 9 on whrch are mounted pole pieces 11 and 12 carrying coils 13 and 14 respectively, The magnetic structure is preferably the same as that described in Patent No. 1,273,351 of July, 23, 1918 to H. A. Frederick. Screwed to the case 10 is a ring 15 to which is attached by welding, or other suitable means, an armatureor reed 16 in operative relation to the pole pieces 11 and 12. The armature 16 is shown as a narrow reed secured at both ends. Although :3. diaphragm of the usual type may be used, the narrow armature is preferable as it does not pick up sound vibrations from the air so readily. Attached to the armature 16 by cement or other suitable means is a coupler or mechanical transformer 17, consisting of a mass of soft elastic material such as gum rubber for making direct contact with the body. As shown, the coupler 17 is in the form of a truncated cone about inches high with bases about inches and 1 inches in diameter. The larger base is attached to the armature 16 and is smaller in diameter than the opening in the ring 15 leaving a small annular opening therebetween. Preferably, the coupler 17 is in contact with the entire outer surface of the armature 16, thereby contributing high damping to the small vibrations of the latter. The natural period of the member 17 and .the armature 16 thus coupled together is uite low bein less-than 300 cycl s er sec- End and when placed against tluf flgsh the whole vibratory system is substantmlly aperiodic. A vibratory system of th1s type will therefore readily detect both the high pitched systolic and diastolic sounds made up of frequencies between 120 and 700 cycles per second, very high pitched components of certain murmurs and ofratio sounds up to 1500 cycles per seecond'. and the normal heart sounds, fetal heart sounds, or presystolic murmer sounds which are composed primarily of energy of relatively low frequencies.

In order to revent the transmission of hand tremors oi the auscultator and to preclude friction noises which would otherwise be caused by the rubbing of the fingers on the case 10, the device may be provlded wlth a flexible handle or holder 18. This holder may be made of any suitable yielding material and a variety of sha es ma be used depending upon the fiexibllity o the material employed. As shown it is composed of soft rubber in the form of an annulus which may be slipped over the case of the instrument. The inner edge 15? and the outer edge 20 which are comparatively thick are connected by a thin web 21. At the point where the usual telephone conductors enter the case, the annulus is cut away to prevent rubbing contact with the conductors which would introduce objectionable fr1ction noises.

The device shown in Figs. 3 and 4 is substantially the same as that shown in Figs. 1 and 2 except a plate 22 is disposed at the back of the reed 16 to close the case andthe ring 15 is provided with an adjustable cylindrical fian e 23 which permits compression of the flesh without freezingthe armature when it is necessary to applypressure to the detector to get closer to thesource of sound, as in fetal heart auscultation. It is also useful in strap ing the detector on the patient when ma ing phonograph records or cardiograms.

Figs. 5 and 6 show another form of the detector which, on account of its small size, is especially suitable for the internal exlorations, such as the early detention of fetal heart sounds. The coupling means 24 and the armature 25 may be the same as the members 17 and 16 respectively, for the device hereinbefore described, except for size.

The relative sizes are substantially as shown in the drawing. The magnetic system is the well-known electromagnetic type. The coil 26 is mounted on a pole 27 secured to a case 28 which forms part of the magnetic circuit. The detector is held in a soft rubber cup 30 the wall of which is sufficiently -may also be used in tlie rectly through the switches 57, 58 and 56 thin near the bottom to preclude the transmission of longitudinal vibrations from the handle 29 of hard rubber or other suitable material, attached thereto. A longitudinal opening for the leads or conductors from the detector is provided in the handle 29. A casing 31 of dental dam rubber is pro vided for the completed device... For special observations, it is sometimes of advantage to provide a vibratory member which is most eflicient at the frequency of the vibrations to be observed. This may be readily accomplished by loading the rubber coupler 24 with lead ellets 32, or other suitable material, as s own in Fig. 6. Obviously the same method of loadin the vibratory system detectors shown in Figs. 1 and 2 and 3 and 4. Although the detector 26 is shown as having its axis coincident with that of the handle 29 in most cases it will be set at a slight angle to permit the survey of a large area by turning the handle 29.

In the system shown in Fig. .7 the sound vibrations are picked up bythe detector 50 of any of the forms herein described and translated into electrical vibrations. The electrical vibrations are then amplified by means of amplifying vacuum tubes 51 and 52 connected in any well known manner. Any number of vacuum tubes may be used depending upon the amount of amplification desired. Between the output of the last stage of amplification and the translating device 53 there may be connected by means of suitable switches 57 and 58 a series of low and high pass filters 54 and 55. While only two filters are shown there should be a sufficient number having different characteristics to give a suitable variety of frequency bands for permitting observation of the different classes of sounds of interest inauscultation and suppressing all extraneous sounds outside of these bands. Any suitable form of wave filters may be used, such as those described in Patent No. 1,227,113 of May 22, 1917, to G. A. Campbell.

As shown the translating device 53 is the usual head telephone receiver connected dito the output of the-amplifier 52 for general observation of all body sounds.

By manipulating the filter switches any desired combination of filters may be obtained. It is therefore possible to subdue to any desired degree extraneous noises and such of the body vibrations as are not of im mediate interest.

It is obvious that any suitable translating device such as a recording device or a loud speaker may be employed.

-It is also often desirable to permit a large number of persons to listen to the vibrations at the same time, especially for teaching and consulation. A loud speaking re- 1319 'ceiver may he used for that purposepr each observer may be provlded wlth an 1nd1v1dual receiver. When a plurality of instruments are used it is preferable to connect them throu h a transformer 59 whlch ma be connected in circuit by means of a swltc 56. Preferably the secondary of the transformer is tapped so as to compensate for variation in the number of instruments connected to the jacks 60. The examining ph sician may transmit remarks other 0 servers by talkin directly aga1nst the flesh of the patient w ile the detector is resting against it. It is preferable to disconnect the filters while transmitting speech sounds.

This apparatus may also be connected to an ordinary telephone or other communlcation system permitting d agnosis by an absent physician or consultation by a number of absent physicians thus expediting matters in serious or unusual cases.

By connecting a plurality of recording devices and assoclated filters in multiple, it is possible to record simultaneously any number of frequency components of the vibrations originating inthe body.

Although the invention is illustrated with soft rubber any other material having the proper characteristics may also be used and microphones and other types of detectors may be used in place of t e magnetic type. The magnetic detector is, however, preferable on account of its inherently higher quality, and the absence of annoying carbon noism which tend to mask the faint sounds of pathological interest.

The arrangement of the parts comprising the detector may also be reversed by making the body-contact vibratory system consist of the magnetic system supported in the case by means of a suitable spring, with the pole pieces of said magnetic system in operative relation with a non-flexible member attached to the case.

What is claimed is:

1. In a stethoscopic device a casin a flexible member supported therein, and a relatively heavy mass of material having the mechanical properties of soft rubber secured to said flexible member and adapted to make contact with the body for detecting sound vibrations originating therein.

2. In a stethoscopic device, a casin a narrow vibratory reed supported at 0th ends in said casing, and a mass of soft rubber secured to said reed and adapted to make contact with the body, whereby sounds originating therein may be detected.

3. In a stethoscopic device, means for converting sound vibrations into electrical vibrations including a flexible member and yielding means having a characteristic impedance to sound vibrations slightly greater than that of the flesh.

4. In a stethoscopic device, a vibratory member, and a mass of yielding sound con- I ducting material having a mechanical impedance slightly less than that of the viratory member.

5. In a stethoscopic device a flexible member, a mass of soft elastic material for making contact with the body supported on said flexible member and substantially its free area.

6. In a stethoscopic device a casing having a circular opening therein, a narrow vibratory member supported across said opening, a mass of soft elastic material su ported on one side of said vibratory member out of contact with said case, and adapted to make contact with the body.

7. In a stethoscopic device a casing havin an opening therein, an electromagnet in sai casing, a vibratory armature in operative relation to said electromagnet, a truncated conical mass of soft rubber supported on said armature and substantially closing the opening in said casing, said mass of soft rubber being adapted to make contact with the body.

8. The combination of an electrical stethoscopic device with a soft rubber support surrounding said device thereby substantially insulating it from vibrations due to relative motions between the patient and the ausculatators hand.

9. In an electrical stethoscopic device the combination of an electromagnetic detector for converting mechanical vibrations into electrical vibrations, the vibratory system of said detector having an im edance to sound vibrations substantially t e same as that of flesh, an amplifier for amplifying said electrical vibrations, and ad ustable electrical filters for assing only the vibrations to be observed and means for convertin the passed vibrations into observable e ects.

10. In a stethoscopic device, a vibratory system having a low natural period, said system comprising a vibratory member, a mass of soft elastic material secured thereto, and a material of greater density embedded in said elastic material.

11. In a stethoscopic device a vibratory system comprisin a vibratory member, a mass of soft elastlc material secured to the face thereof, a casing for said vibratory system, a cylindrical extension therefrom adapted to compress the flesh while said elastic material is in contact therewith.

12. An electrical stethoscopic device comcovering I prising a vibratory element and a contacting element of soft elastic material adapted to make contact with the body said elements having suflicientl 'large values of mass and stiffness to give t em a natural period below 300 cycles per second frequency.

13. An electrical "stethoscopic device having a vibratory system for making direct mg a flexible member and a mass mounted thereon, the im edance looking into said system being su stantially the same as the impedance looking into the flesh with which it makes contact.

14. In a stethosco ic device, a vibratory member adapted to e vibrated in response to sound vibrations within a patients body, and means comprising a soft elastic medium for directly transferring vibrations from contact with the body said system compris- 

